如图，在▱ABCD中，E是CD的中点，AE的延长线与BC的延长线相交于点F．
求证：BC=CF．
The computer company just released an ____ (更新) version last week, and it'll be used in over 50 local classrooms this coming school year.
如图，一束光线与水平面成30°角斜射到水面上，同时发生反射和折射，请在图中画出反射光线和折射光线的大致方向，标出反射角的度数．
